Influencing factors of drainage dynamics of CBM wells and primary drainage rate optimization in East Yunnan-Western Guizhou area

Based on the data of more than 40 wells(12 drainage wells) in East Yunnan-Western Guizhou area,the in- fluencing factors of drainage dynamic in Enhong,Laochang and Tucheng blocks are discussed through the ex-traction of drainage dynamic typical indexes of CBM wells and the comprehensive analysis of geological and engineering fac- tors,combined with numerical simulation and the primary drainage rate optimization steps are finally put forward. The results show that there is a great difference in the drainage dynamic of CBM wells in the study area. The producing re- source abundance and permeability determine the gas production capability of CBM wells as basic factors. The higher the producing resource abundance and the permeability are,the higher gas pro-duction is. Meanwhile,the reservoirs with coal body structure Type I and II have a higher gas production compared to that with coal body structure Type III. The primary drainage rate is the key controlling factor of drainage dynamics of CBM wells. When the primary drainage rate is relatively high,even with the permeability and the producing resource abundance being high,the gas production is still relatively low. Controlling the primary drainage rate has two meanings:one is to slow down the reduction of ab- solute permeability(stress-sensitive),and the other is to delay the occurrence of two-phase flow,both having objective to extend the depression cone to maximum. Based on the above understanding,it is pointed out that slow drainage should be key in the study area. A low rate-ladder type pressure reduction,during primary drainage,is proposed. This pressure reduction regime has a certain practical significance for co-production from multiple-coalbeds in East Yunnan- Western Guizhou area.